Number, String

Numbers

• Division (/) always returns a float.
• The equal sign (=) is used to assign a value to variable.
• If a variable is not 'defined' (assigned a value), trying to use it will give you an error.
• In interactive mode, the last printed expression is assigned to the variable _.
• supports types of numbers, such as int, float, Decimal and Fraction.
• also has built-in support for complex numbers, and uses the j or J suffix to indicate the imaginary part (e.g. 3+5j).

>>> 8 / 5   # division always returns a floating number
1.6

>>> 17 // 3  # floor division discards the fractional part
5

>>> 17 % 3   # the % operator returns the remainder of the division
2

>>> 5 ** 2   # 5 squared
25

>>> 2 ** 7   # 2 to the power of 7
128

Strings

• can be enclosed in single quotes('…') or double quotes (“…”)
• \ can be used to escape quotes:
• String literals can span multiple lines.
  • “”“…”“” or '…'
  • it's possible to prevent including end of lines by adding a \ at the end of the line
• Python strings cannot be changed – they are immutable.

>>> 3 * 'a' + 'bcd'
'aaabcd'
>>> 'Py' 'thon'
'Python'

>>> text = ('Put several strings within parentheses '
...         'to have them joined together.')
>>> text
'Put several strings within parentheses to have them joined together.'

>>> prefix = 'Py'
>>> prefix 'thon'  # can't concatenate a variable and a string literal
  File "<stdin>", line 1
    prefix 'thon'
                ^
SyntaxError: invalid syntax

>>> ('a' * 3) 'bcd' # SyntaxError

>>> prefix + 'thon'
'Python'

>>> word = 'python'
>>> word[0]
'p'
>>> word[5]
'o'
>>> word[-1]
'n'
>>> word[0:2]
'py'
>>> word[2:5]
'tho'
>>> word[:2] + word[2:]
'python'

>>> word[100] # IndexError
>>> word[4:100]
'on'
>>> word[100:]
''
>>> len(word)
6